The use of a cursor control device to control a cursor on a display screen of a digital processing system has become almost universal. The cursor control device, commonly a mouse, trackball, or stylus device, is actuable by a user to generate a signal when transmitted to the digital processing system. The digital processing system then utilizes the signal to control the cursor on the screen. For instance, the cursor may be used to select an object on the screen, move the selected object on the screen, scroll an on-screen document, etc.
Typically, when moving the object on the screen, the user first points the cursor to the object using the cursor control device. Then, the user activates a switch (e.g., a mouse button) of the cursor control device to hold the cursor on the object (e.g., by pressing the mouse button) and moves the cursor control device as necessary to get the object into a desired position while keeping the switch in the activated position. Once the object is at the desired position, the user deactivates the switch (e.g., by releasing the mouse button). However, when moving the cursor control device, the user may reach the end of the surface on which the cursor control device is moved (e.g., a mouse pad, a computer desk, etc.) before the object gets to the desired position on the screen. In this situation, the user would typically lift the cursor control device from the surface when reaching the end of the surface and reposition the cursor control device on the surface in order to continue moving the cursor control device until placing the object at the desired position. It is common for users to unintentionally deactivate the switch (e.g., by releasing the mouse button) while lifting the cursor control device.
Existing cursor control devices do not allow the user to extend selection of the object after deactivating the switch due to a necessary repositioning of the cursor control device on the surface. As a result, the user loses the object and must reinitiate the selection of the object on the screen, thereby causing the inconvenience to the user and slowing the move operation. In addition to the above disadvantages, forcing the user to constantly keep the switch of the cursor control device in the activated position (by, for example, constantly keeping the mouse button down) while manipulating with the cursor control device is ergonomically undesirable. Thus, it would be advantageous to provide a mechanism allowing to keep the cursor on the object while lifting the cursor control device in the air to reposition.
In order to extend holding capability while lifting the cursor control device in the air, the digital processing system should receive a signal indicating that the cursor control device has been lifted from the surface. Known cursor control devices include mechanical switches to detect an off-table movement. For example, a mouse may rely on a mechanical tracking ball to indicate that the mouse is off the table. However, mechanical switches are not always reliable because they depend to a significant degree on a fairly delicate compromise about how mechanical forces are developed and transferred. In addition, mechanical switches do not provide a sufficiently fast indication of an off-table state of the cursor control device. Furthermore, mechanical switches require mechanical coupling to the surface and are subject to mechanical wear. Therefore, it would be desirable to provide a reliable non-mechanical off-table switch which will quickly signal the lifting of the cursor control device from the surface.